A breath test might show it's not your fault you're fat

Researchers trying to figure out if microbes living in your body might be a factor in weight gain say a breath test could show if you’re loaded with greedy germs that pull every last calorie out of food.

Study after study is showing that people are covered in bacteria, fungi and other microorganisms that help digest food, that can keep teeth healthy and even that cause dandruff. And they’re finding that the types of microbes living in the colon and intestines may play a major role in just how much nutrition the body gets out of food.

“Normally, the collection of microorganisms living in the digestive tract is balanced and benefits humans by helping them convert food into energy,” says Dr. Ruchi Mathur, an endocrinologist at at Cedars-Sinai Medical Center in Los Angeles.

Mathur and colleagues were looking at a species of bacteria called Methanobrevibacter smithii – M. smithii for short. As its name indicates, it makes a lot of methane – the odorless gas responsible for burps and other inconvenient emissions.

People who produced the most methane and another gas, hydrogen, in their breath weighed more and had more body fat than people who produced the lowest amounts, they reported in the Journal of Clinical Endocrinology & Metabolism.

“This is the first large-scale human study to connect the dots and show an association between gas production and body weight,” Mathur said in a statement.

The team tested 792 volunteers, dividing them into four groups – those with “normal” levels of gases in their breath, those who had more methane than average, those who breathed out more hydrogen than average and those who produced extra amounts of both methane and hydrogen.

Those in the last group, exuding the highest concentrations of both hydrogen and methane, also had higher body mass indexes or BMI, the standard measure of height to weight that doctors use to determine obesity. They also had more body fat than the others.

This fits in with other work Mathur’s team has done on the role of this particular bug in obesity, they noted. For one, obese people with more methane detectable in their breath weighed nearly 15 pounds more than other obese people who didn’t produce as much methane.

M. smithii needs hydrogen, and it gets it from other bacteria living in the gut, which produce hydrogen gas as a byproduct of metabolizing food. The researchers are not entirely sure how a methane-producing bug might make people fatter, but said it’s possible methane gas slows the passage of food through the intestines and colon, allowing more calories to be extracted.

Diet could affect this, and the researchers didn’t ask their volunteers for details about what they ate. “However, given the large sample size, these individual variations may be mitigated between groups,” they wrote.

Researchers are trying to figure out if it’s possible to kill off the guilty germ and help people lose weight. But they know better than to just kill gut bacteria willy-nilly – studies have shown that taking antibiotics can alter the balance of microbes in a bad way, causing stomach upset, allowing deadly infections such as C. difficile to take hold and, perhaps, even allowing a takeover by the obesity-generating germs.